The CD45 antigen family is a group of high molecular weight glycoproteins that are expressed on the plasma membranes of all leukocytes. CD45 has protein tyrosine phosphatase activity and appears to regulate signal transduction and lymphocyte activation by specific association with receptor molecules on T and B lymphocytes. However, little is known about CD45 function in neutrophils (PMNs). In this study, PMNs were incubated with CD45 monoclonal antibodies (mAbs) and tested for their chemotactic responses to four unrelated chemoattractants: N-formyl-methionyl -leucyl-phenylalanine (FMLP), leukotriene B4 (LTB4), recombinant human C5a (C5a), and recombinant human neutrophil activating protein-1 (NAP-1), recently designated as interleukin 8 (IL8). A panel of CD45 mabs including an IgM mAb, AHN-12.1, and six IgGl mAbs, AHN-12, AHN-12.2, AHN-12.3, AHN-12.4, HLe-1, and KC56(T200), were tested for their effects on PMN chemotaxis. PMN chemotaxis.was evaluated with two different membrane assays: one assay quantified the.total number of migrating PMNs and the other assayed the leading front of migrating PMNS. AHN-12.1 and KC56(T200) significantly inhibited PMN chemotaxis to LTB4 and C5a. AHN-12.1 also inhibited PMN chemotaxis to FMLP, but KC56(T200) did not. In contrast, AHN-12 and HLe-1 did not significantly inhibit PMN chemotaxis to any of the chemoattractants. None of the CD45 mAbs inhibited PMN chemotaxis to NAP-1/ IL8. These results indicate that PMN CD45 epitopes may interact with LTB4, C5a, and FMLP receptors or receptor-associated molecules and regulate chemotactic responses. The results of this study were presented at the American Society for Biological Chemistry and the American Association of Immunologists Joint Meeting, June 3-7, 1990, New Orleans, LA.